Recently, various types of portable electronic devices have been gradually widespread according to rapid development of miniaturization techniques for electronics devices. Batteries that are power supplies of these portable electronic devices are required to be miniaturized. A nonaqueous electrolyte secondary battery having high-energy density has attracted attention.
In particular, attempts to use elements to be alloyed with lithium, such as silicon and tin, and a material, such as amorphous chalcogen compound, having large lithium occlusion capacity and high density, have been made. Particularly, silicon can occlude lithium by a ratio of 4.4 atoms of lithium to one atom of silicon. Negative electrode capacity per mass is approximately ten times that of graphite carbon. However, silicon has a problem with cycle characteristics, such as pulverization of active material particles, due to a large variation of volume in accordance with insertion and separation of lithium in a charge and discharge cycle.
As a result of eager experiments, the present inventors have found that an active material dispersed in a carbonaceous substance can be obtained in a state where microcrystalline silicon has been included in or retained by silicon oxide firmly bonding with silicon, in the minute active material including silicon monoxide and the carbonaceous substance complexed and calcined. The present inventors have found that large capacity and improvement of the cycle characteristics can be achieved. However, when several hundred charge and discharge cycles are performed to this type of active material, the capacity degrades. Thus, the cycle characteristics are insufficient for use during a long period.
In order to solve this problem, the present inventors have thought that properties of the carbonaceous substance have a large influence with respect to the cycle characteristics. The present inventors have examined that another material is used instead of the carbonaceous substance. This type of material is required to have conductivity and is also required to be a material that disperses particles containing the above type of microcrystalline silicon, inside.